Confined or space resonance antenna



M y 8, 1940. H. E HOLLMANN 2,202,380

CONFINED 0R SPACE RESONANCE ANTENNA Filed Nov. 11, 1937 INVENTOR MAR/I01 ANN BY ATTORNEY Patented May 28, 1940 UNITED STATES CONFINED OR SPACE RESONANCE ANTENNA Hans Erich Hollmann, Berlin,

to Telelunken Gesellschaft graphic m. b. It, Berlin,

tion of Germany Application November 11, 1937, Serial No.

Germany, asslgnor liir Drahtlose Tele- Germany, a corpora- In Germany August 27, 1936 6 Claims.

If a radiating antenna or radiator, say, a dipole, is mounted inside a space which is practically completely closed and which has metallic boundary walls, provided that the space is of such proportions that standing waves will be set up therein, the space will act in respect to the antenna like a sounding board. The result is that the coupling between the antenna and the ambient air space is reinforced and thereby the radiation of the antenna is effectively increased.

The situation will be most clearly understood and the underlying actions also be most effective in the case of a space or enclosure having a form as simple as feasible and adapted to the form of the antenna. Preferably the enclosing wall will be in the form of a hollow cylinder, in the axis of'which the nating surfaces or faces of the said enclosure being closed either at one end or at both. If desired both ends may be left open. ideal case, that is, of an infinitely long cylinder having walls of infinitelyhigh conductivity, theoretical considerations determine the definite critical cylinder radii for which space resonance oc- 25 curs. These may be calculated on basis of the following relation where kn, the zeros of Bessel cylindrical functions of the first kind of 0th order, are:

I61 I02 I63 764 2.40 5.52 8.65 11.79

For the higher ordinal numbers (n=1, 2, 3 the partial waves form nodal planes or surfaces which have the shape of concentric cylinders.

The invention is further explained with reference to'the accompanying drawing, Figs. 1 to 3, which show various modifications of the invention. r

In practice, of course, the cylinders may have a length of only a few waves, and since energy transportation occurs only in an axial direction with respect to the cylinder, appreciable radiation of energy will occur at the open ends of the cylinders. The graph in Fig. 1 shows the meridian section through the radiation diagram which results in the case of the first critical radius. Evidently, the radiation maxima are perpendicular to the cylinder axis, and this may be explained by the fact that the radial field components are negligible throughout withrespect to the axial field components. The Poynting vectortherefore points outwardly with respect to the cylinder axis. The space radiation antenna is disposed, the termi- In the diagram is obtained byrevolving the meridian section about the cylinder axis.

Closing the lower end of the cylinder with a metallic counter plate, the radiation emerging through the open end is roughly doubled. Hence, space resonance is an efficient means of appreciably raising the radiated energy or the radiation resistance of a dipole antenna.

As may be noted from the above formula for the critical diameters, the diameter of the cylinder enclosing the antenna, even in the most favorable instance of the first critical radius, is equal to half the length of the operating wave. Since, moreover, the cylinder, in axial direction must-have a length of several waves, it follows that space resonance may be considered in practice only for comparatively short waves, lest the proportions of the antenna structure become awkward.

In order that the dimensions of the resonance- -reinforcing space may be reduced in both radial and axial direction so that space resonance may be practically utilizable in the case of waves of a few meters length, or that alternatively the higher values for the critical radii may be within reasonable limits, it is suggested, according to another object of the invention, to fill the resonant space, with a low-loss medium possessing a high dielectric constant. Assuming that the entire inside space of the cylinder is filled with a homogeneous dielectric substance having a dielectric constant e, the wave as compared with 4 air as the dielectric, will be shortened in proportion to and thus the critical cylinder radii will be )ckn 21r For instance, if the cylinder were filled with distilled water which has a dielectric constant of 81, this will result in a shortening of the wavelength and thus also the critical radius to oneninth. The same situation holds good in regard to the axial cylinder length. Since the waves are reflected at each and every layer where the dielectric constant experiences a marked and abrupt change, space resonance will be brought about in this case also when the cylindrical dielectric is not confined inside a metallic casing, but fills up an insulator casing or is freely bounded in reference to space. The latter case is, of course, possible only where a solid dielectric sub-' stance is dealt with.

However, it is for this same reason that the waves are not ableto emerge from the dielectric forming a complete boundary in reference to the surrounding air space, since, just as inside a completely closed space, they are reflected from all boundary walls or surfaces. In short, the antenna is for all practical purposes completely shielded, and it is unable to give off any useful signal radiation into surrounding space.

Therefore, in order that the space waves generated inside a dielectric having a high dielectric constant may be afforded a chance to emerge and issue into the surrounding air, a suitable outlet hole or outlet plane, according to this invention is created in such manner that any sudden change in the dielectric constant in the direction of the cylinder axis, is practically entirely avoided. This is done by subdividing the medium into a plurality of layers or strata presenting steadily decreasing dielectric constants until finally a value equal to that of the ambient air, i. e., unity, is reached. Since thus, for each one of the various layers, there result diiierent critical radius values, it follows that the radii of these layers must be increased at the ratio of Ma an-Vilma From the cylindrical shape, one thus gets the form of a cone or funnel as shown in Fig. 2. In the figure the constituent layers which form the transition in a practically continuous manner from the space I filled with distilled water and in which the antenna D is located, to the outside air, are designated by S1, S2, S3 $5, the corresponding dielectric constants being 6 e 6 e, For these various layers are chosen liquids or substances whose dielectric constants become steadily smaller with rising index s. The critical radius applying to each individual stratum thus follows from the formula:

The cylinder containing the antenna, because of its dielectric constant being 81, is of the smallest diameter. In accordance with the decrease in the dielectric constant, the critical radii of the constituent layers will become so much greater, the closer the layer under consideration is to the outside air, until finally the last layer reaches the critical radius which was found by the aid of the above law for air, i. e., 5:1. In order that points of unsteadiness irregularity may be avoided in the wall of the cone or funnel, the latter is not set-off in stages or terraced, but presents an uninterrupted expansion or flare. The shape and the rate of expansion of the funnel wall thus is not fixed by any'definite law, but it is entirely governed by the choice of the various consecutive layers. The layers should preferably be made thicker as the dielectric constant thereof decreases whence an exponential or logarithmic law results for the funnel. I

In view of the fact that the dielectric constants of the last few layers approaches unity, it is preferable to demarcate the funnel by a metallic reflector wall in reference to air in order that the property of space resonance may be preserved as far as the outermost layers.

Fig. 3 finally shows an arrangement for the purpose of feeding the antenna D in the simplest possible manner through a concentric or co-axial feeder line B. terminating in the funnel from below. The middle conductor projects beyond the outer sheath of the feeder line and constitutes the antenna proper. Such a funnel antenna may be mounted upon the feeder line without additional support thus providing an extremely simple and effective non-directional radiator. Of course, it desired there is no difficulty in mounting the funnel antenna in the focus or in the focal line of a suitable reflector in order that the radiation may be concentrated in the equatorial plane.

I claim:

1. A radially directive antenna comprising a vertical conductive tube closed at one end and open at the other end and a radiating member mounted inside said tube along the axis thereof near the closed end, said tube being filled with a medium having a high dielectric constant around said radiator and a steadily decreasing dielectric constant between the radiator and the open end of the tube.

2. An antenna comprising a conductive tube closed at one end and open at the other end and a radiating member inside said tube along the axis thereof, said radiating member surrounded by a medium having a high dielectric constant and said tube having layers of dielectric material oi successively decreasing dielectric constants in consecutive order between the end of the radiator and of the tube varying inversely as the dielectric constant of the material in the tube.

3. A space resonance antenna comprising an elongated radiating member confined inside a space which is filled with a medium possessing a high dielectric constant, said space being so dimensioned that it is tuned to the operating wavelength of said antenna, and means for conveying energy from said space comprising layers of dielectric material placed in consecutive order along the axial direction of said radiating member, said layers having a steadily decreasing dielectric constant with increasing distance from said radiating member.

4. A space resonance antenna as claimed in claim 3, in which the diameter of the various layers increases in the direction from the radiating member in inverse proportion as the square root of the dielectric constant thus resulting in the form of a funnel.

5. A radially directive antenna comprising a vertical tube closed at one end and open at the other end and a radiating member mounted inside said tube along the axis thereof near the closed end, said tube being filled with a medium having a high dielectric constant around said radiator and a steadily decreasing dielectric constant between the radiator and the open end of the tube.

6. A radially directive antenna comprising a vertical non-conducting tube closed at one end and open at the other end and a radiating member inside said tube along the axis thereof near the closed end, said radiating member surrounded by a medium having a high dielectric constant, the radius of said tube being such thatspace resonance occurs for the frequency transmitted and said tube having layers of dielectric material of successively decreasing dielectric constants in consecutive order between the end of the radiator and the open end of the tube.

HANS ERICH HOLLMANN.

the open end of the tube, the diameter Bill 

